Supermarket buy-one-get-one-free deals and multi-buys are fuelling climate change because they result in millions of tonnes of unwanted food being binned each year, it was claimed this week.

About a third of the 20 million tonnes of food purchased by UK households every year is sent to landfill where it produces methane - a gas 23 times more environmentally damaging than carbon dioxide, according to a new report by Wrap.

It identifies special offers such as bogofs as one of the key drivers for food wastage. Thirty per cent of respondents who admitted to regularly throwing away food said this was because special offers had tempted them to buy more than they needed. "Shoppers are purchasing more food than they need, and certain promotions, such as bogofs and two-fors, contribute to this," said Mark Barthel, adviser for retail and innovation at Wrap.

The report also found consumers were more susceptible to special offers due to the trend towards top-up shopping, said Barthel.

"People tend to impulse buy, without checking what they already have in the fridge, leading to duplicate purchases and wastage."